The present invention relates to a motor having a plain bearing, especially a cup and ballbearing, for a rotor shaft whose axial play is adjusted. The invention also relates to an associated method for adjusting the axial play of the rotor shaft.
The rotor shafts of mass-produced motors, whose stators include several components, may have an impermissible axial play. The axial play may be too high due to tolerances of the individual components of the motor. Therefore, when the motor is assembled, there is a need in the art to adjust this axial play of the rotor shaft to a pre-defined permissible range.
European Patent Application EP 0 592 303 A1 discloses a motor, which has a cup and ballbearing. The cup and ballbearing can be adjusted axially in a bearing receiver by means of a single clamp holder. In its operating end position, the cup and ballbearing can be fixed by a claw. To do this, the single clamp has two types of radial fingers distributed around its circumference. Specifically, fingers that are bent inward to hold the plain bearing in an embracing manner alternate with fingers having claw ends that project radially outward to fix the clamp in the bearing receiver.
U.S. Pat. 3,770,990 teaches a bearing arrangement for a shaft. A spherical cap is mounted on each end of the shaft. Each of the spherical caps, which contact respective clamp holders, is divided in two axial parts. Together with the shaft, one of the parts of a respective spherical cap can be rotated relative to the other, resting part in order to compensate for any radial play.
German Patent DD 259 504 A1 teaches a fastening for plain bearings that compensates axle displacements, wherein the plain bearings are located in plastic end shields. In this method, a pendulum plain bearing is, on one of its axial face sides, fixed in axial direction by means of a pressure disk that is held in a bearing shaft. At its other axial face side, the pendulum plain bearing is pressed, with elastic stress, against a spherical ring surface of the end shield.
It is one object of the present invention to provide a simpler adjustment of an axial play of rotor shafts of mass-produced motors in order to reduce the expenditure for manufacturing and assembling these motors. A further object is to provide a simple adjustment for motors in which the respective rotor shaft is rotatably borne in a plain bearing, in particular a cup and ballbearing, while an optimal damping of axial vibrations of the rotor and an operationally safe adjustment of the plain bearing is ensured. While the present invention is not limited to a specific type of plain bearing, it is another object that the simplified adjustment is suitable if the plain bearing is embodied as a spherical cap, for example.
According to one formulation of the present invention, these and other objects are achieved by a motor which has a plain bearing to adjust an axial play of a rotor shaft of the motor. The motor includes a stator; a first clamp holder which is arranged at one axial face side of the plain bearing; and a second clamp holder which is arranged at the other axial face side of the plain bearing. Therein, the spring stiffness of the first clamp holder is higher than the spring stiffness of the second clamp holder. A bearing receiver receives the first clamp holder, the second clamp holder, and the plain bearing. The first clamp holder and the second clamp holder are, independently of each other, moved to a respective operating end position in the bearing receiver, where they are fixed. Therein, the first clamp holder contacts the one axial face side of the plain bearing in order to adjust the axial play between the rotor shaft and the stator of the motor, wherein the rotor shaft is borne in the plain bearing. The second clamp holder contacts the other axial face side of the plain bearing in order to exert an elastic pressure against the plain bearing and against the first clamp holder.
According to another formulation of the present invention, these and other objects are achieved by a method for adjusting an axial play of a rotor shaft of a motor. In a first step of the method according to the present invention, the rotor of the motor is positioned relative to the motor housing. In a second step, the bearing receiver is fixed relative to the motor housing in that, at the axially inner end of the bearing receiver, the second clamp holder is inserted in the bearing receiver and moved to a second operating end position, where the second clamp holder is fixed. At the axially outer end of the bearing receiver, the plain bearing and the first clamp holder are axially inserted into the bearing receiver. The first clamp holder is moved to a first operating end position in order to adjust a pre-defined axial play of the rotor shaft. At the first operation end position, the first clamp holder is fixed.
Using very simple, standard clamps, the motor according to the invention permits a simple adjustment of the axial play of the rotor shaft of the motor. The axial play adjustment is carried out by axially displacing the first clamp holder when the motor is assembled. Thereby, an adjustment over even long axial adjusting paths is achieved. At the same time, an optimal damping of axial vibrations is ensured. Due to the provision of the second, easily-to-install clamp holder, whose spring characteristic is designed independently of the first clamp holder, the danger of a loose plain bearing is avoided. The plain bearing can be a spherical cap, for example. In a particularly simple manner in terms of manufacturing the clamp holders, each clamp holder includes a clamp that has a radially outer, closed clamping edge. Furthermore, fingers, which project inwardly from the clamping edge, touch the plain bearing.